1. Field of the Invention
The present invention proposes an optical coherence tomography system for the examination of human or animal tissue or organs of the type including a catheter that is insertable into the tissue or organ, by which light is introduced into the tissue or organ and the reflection is transmitted to an evaluation unit, where the reflection and a reference light are evaluated interferometrically to generate a two-dimensional cross-sectional view of the tissue or organ, wherein the evaluation unit uses several two-dimensional cross-sectional views to derive a three-dimensional view of the tissue or organ, and wherein at least one position sensor is disposed on or in the tip of the catheter, as part of a position-determining system for deriving position data describing the current position of the position sensor in the coordinate system of the position-determining system.
2. Description of the Prior Art
Optical coherence tomography (OCT) is a medical examination modality, in which two-dimensional cross-sectional views of the object to be examined are obtained by shining light via a catheter into the object and then analyzing the reflection. In a method similar to B-mode ultrasound, light is emitted and the tissue or organ reflection is analyzed to derive information about the structure of the illuminated object. The depth information, i.e. the visual information about the tissue or organ, is derived in coherence tomography by means of interferometry with a reference light source of known length. The length of the reference light source is modified constantly. The interference at the interferometer corresponds to object points in the examination light ray, for which the reference ray and the examination light ray measured to the object point in question are of equal length. Light is introduced into the tissue by means of a thin catheter with a diameter of 1 mm or less. Consequently, optical coherence tomography may be used wherever a catheter may be inserted. Examples include, but are not restricted to, views of the inner surface and outer surface of vessels, the gastrointestinal tract, the urogenital tract, the eyes or the skin.
Optical coherence tomography yields two-dimensional cross-sectional views from scanning by means of the light ray emitted from the catheter, which rotates to generate a local cross-sectional view. Thus, it is a ring or annular view with a rotating light ray, primarily a laser. The doctor sees a two-dimensional cross-sectional view of the just-scanned area in real time. A method is known to derive a three-dimensional view of the vessel or organ from a number of two-dimensional cross-sectional views and to display it on a monitor in order to give the doctor a three-dimensional view of the vessel or organ for better diagnostic evaluation. Thus the doctor can see a three-dimensional view of the examined organ based on the many two-dimensional cross-sectional views. The three-dimensional view simplifies the estimation of the three-dimensional extent of anatomical structures and any pathological processes that are present.
A disadvantage of known coherence tomography systems is the lack of information regarding the relative position of the individual cross-sectional views, as the derivation of the three-dimensional view treats the cross-sectional views as parallel to each other. Consequently, the vessel, which is coiled and non-linear, is shown as a linear three-dimensional unit. The doctor will in fact see a three-dimentional view, but that view does not show the true three-dimensional extent and the path of the vessel or organ being examined, thus also not the length, width and actual location of any pathological structures present. As a result, the three-dimensional views impose limits on the quality of the final diagnosis.
German OS 100 51 244 discloses a mechanism for determining the position of a medical instrument introduced into the object being examined, as well as to view the vicinity of the medical instrument, such as a catheter, by means of a position sensor located in the tip of the instrument in conjunction with a position-determining system. A three-dimensional overview of the area where the position sensor is currently located, as indicated by the position sensor, is computed based on a set of three-dimensional view data collected prior to the intervention itself. This three-dimensional overview is transmitted to a monitor. The current position of the position sensor is indicated in this three-dimensional overview. In addition to this three-dimensional overview, the current two-dimensional view taken by the OCT scanner, which is built into the instrument, is also displayed on the monitor.
An article by Y. Zhao et al entitled Three-Dimensional Reconstruction of in Vivo Blood Vessels in Human Skin Using Phase-Resolved Optical Doppler Tomography, IEEE Journal on Selected Topics in Quantum Electronics, Vol. 7, No. 6, pages 931-935, 2001, describes a three-dimensional reconstruction procedure on the basis of optical Doppler tomography views.